Yes, they both tend to be 1:1 with sugar measurements in how they're packaged.
The Erythritol (my favorite of the two) is about 80% sweet of sugar (0.2cal/gram).
Xylitol is 100% sweet of sugar, but does have more calories (2.5cal/gram).
(Sugar is 4cal/gram)
Okay so I'm confused again. It they are both 1:1 with sugar, then they would be equal to each other as well, correct? Why is one sweeter than the other?
Well, guess it depends on how sweet you like things... You'd probably have to go 1:1.25 for the Erythritol, if you're going for the exact sweetness. I like it because it IS less sweet. :-)